A refractory is a ceramic material of low thermal conductivity characterized by the ability to withstand extremely high temperatures. Refractories are used for lining steel furnaces and other high-temperature applications. They are normally cast in the form of brick with some type of binder to assure their stability.
The three groups of refractories include acidic refractories, such as silica; basic refractories, such as magnesite; and amphoteric refractories, such as alumina. In recent years, there has been an increased demand for refractory articles made from basic materials, such as magnesia.
Phenolic resins are widely used as refractory binders. However, they have certain drawbacks when used as binders for magnesia. When magnesia granules are mixed with conventional resole resins, the mixtures tend to harden in a comparatively short time. This reduces the time that the mix can be retained before it must be shaped into bricks or other desired shapes. Furthermore, the articles produced from these mixtures often show poor strength and durability. The phenolic resole resins themselves also tend to be unstable and may require refrigeration if they are stored for any period of time.
A modified phenolic resole resin has been discovered which does not have the shortcomings of conventional resole resins. This resin can be stored at room temperature for long periods of time without undergoing deterioration. In addition, mixes of magnesite particles and this resin show excellent storage stability. It has also been found that this resin can be used as a binder for acidic and amphoteric particles, such as silica and alumina.